1. Field of the Invention
The present invention relates generally to a semiconductor process for treating a metal gate, and more specifically to a semiconductor process for treating a metal gate applying plasma treatments to reduce metal gates.
2. Description of the Prior Art
Field effect transistors are important electronic devices in the fabrication of integrated circuits, and as the size of the semiconductor device becomes smaller and smaller, the fabrication of the transistors also improves and is constantly enhanced for fabricating transistors with smaller sizes and higher quality.
In one aspect, in the conventional method of fabricating transistors, a gate structure is first formed on a substrate, and a lightly doped source/drain (LDD) is formed on the two corresponding sides of the gate structure. Next, a spacer is formed on the sidewall of the gate structure and an ion implantation process is performed to form a source/drain region within the substrate by utilizing the gate structure and spacer as a mask. In order to incorporate the gate, source, and drain into the circuit, contact plugs are often utilized for interconnection purposes. As the miniaturization of semiconductor devices increases, filling the contact plugs into contact holes has become an important issue to maintain or enhance the performances of formed semiconductor devices.
On the other hand, poly-silicon is conventionally used as a gate electrode in semiconductor devices, such as metal-oxide-semiconductor (MOS) transistors. With the trend towards scaling down the size of semiconductor devices, however, conventional poly-silicon gates face problems such as inferior performance due to boron penetration and unavoidable depletion effect. This increases equivalent thickness of the gate dielectric layer, reduces gate capacitance, and worsens a driving force of the devices. Therefore, work function metals that are suitable for use as the high-K gate dielectric layer are used to replace the conventional poly-silicon gate to be the control electrode.